Ambulatory medical devices include implantable medical devices (IMDs) and wearable medical devices. Some examples of IMDs include cardiac function management (CFM) devices such as implantable pacemakers, implantable cardioverter defibrillators (ICDs), cardiac resynchronization therapy devices (CRTs), and devices that include a combination of such capabilities. The devices can be used to treat patients or subjects using electrical or other therapy, or to aid a physician or caregiver in patient diagnosis through internal monitoring of a patient's condition. The devices may include one or more electrodes in communication with one or more sense amplifiers to monitor electrical heart activity within a patient, and often include one or more sensors to monitor one or more other internal patient parameters. The devices may be implanted subcutaneously and include electrodes that are able to sense cardiac signals without being in direct contact with the patient's heart. Other examples of IMDs include implantable diagnostic devices, implantable drug delivery systems, or implantable devices with neural stimulation capability.
Some examples of wearable medical devices include wearable cardioverter defibrillators (WCDs) and wearable diagnostic devices (e.g., an ambulatory monitoring vest). WCDs can be monitoring devices that include surface electrodes. The surface electrodes are arranged to provide one or both of monitoring to provide surface electrocardiograms (ECGs) and delivering cardioverter and defibrillator shock therapy.
In response to an abnormally slow heart rate or lack of coordination among contraction of the ventricles, some CFM devices deliver electrical pacing stimulation to induce cardiac depolarization and contraction (sometimes referred to as capture of the heart). It is desirable for a physician to know the effectiveness of the pacing stimulation therapy provided to the subject. A system and method for monitoring at least one chamber of a heart during delivery of refractory period stimulation to determine if desired non-capture occurs can be found in Chinchoy et al., “Mechanical Ventricular Pacing Non-Capture Detection for a Refractory Period Stimulation (RPS) Pacing Therapy Using at Least One Lead-Based Accelerometer,” U.S. Patent Application Publication No. US 2008/0269825, filed Apr. 30, 2007. An implantable cardiac rhythm management device capable of automatically detecting intrinsic evoked response of a patient's heart can be found in Zhu et al., Accelerometer-Based Heart Sound Detection for Autocapture,” U.S. Pat. No. 6,650,940, filed Feb. 2, 2008.